Embedded polyzwitterionic brush-modified nanofibrous membrane through subsurface-initiated polymerization for highly efficient and durable oil/water separation

Advanced nanofibers for water treatment: Unveiling the potential of electrospun polyacrylonitrile membranes

The challenges pertaining to the potable water scarcity and pollution motivates us to envision innovative strategies. Industrial wastewater containing hazardous heavy metals, synthetic dyes, and oil exacerbates the pursuit of clean drinking water. Among the array of available technologies, electrospun nanofiber membranes have garnered attention due to their efficiency, high surface-to-volume ratio, cost-effectiveness, scalability, and multifunctionality. These membranes possess distinct physical and chemical attributes that position them as ideal solutions to water purification challenges. Their versatility enables effective contaminant removal through filtration, adsorption, and chemical interactions. Polyacrylonitrile (PAN) emerges as a frontrunner among electrospun polymers due to its affordability, remarkable physical and chemical characteristics, and the ease of production. Research efforts have been dedicated to the study of electrospun PAN membranes, exploring modifications in terms of the functionalization of PAN molecular chain, incorporation of appropriate nanoparticles, and composition with other functional polymers. Parameters such as functional groups, hydrophilicity, mechanical properties, porosity, pore structure, reusability, sustainability, zeta potential, and operational conditions significantly influence the performance of electrospun PAN membranes in treating the contaminated water. Despite progress, challenges surrounding fouling, toxicity, scalability, selectivity, and production costs ought to be addressed strategically to enhance their practicality and real-world viability. This review comprehensively scrutinizes the current landscape of available electrospun PAN membranes in water treatment encompassing diverse range of synthesized entities and experimental outcomes. Additionally, the review delves into various approaches undertaken to optimize the performance of electrospun PAN membranes while proposing potential strategies to overcome the existing hindrances. By carefully analyzing the parameters that impact the performance of these membranes, this overview offers invaluable guidelines for researchers and engineers, thus empowering them to design tailored electrospun nanofiber membranes for specific water purification applications. As the innovative research continues and strategic efforts address the current challenges, these membranes can play a pivotal role in enhancing water quality, mitigating water scarcity, and contributing to environmental sustainability. The widespread application of electrospun nanofiber membranes in water treatment has the potential to create a lasting positive impact on global water resources and the environment. A dedicated effort towards their implementation will undoubtedly mark a crucial step towards a more sustainable and water-secure future.

Tuning Surface Functions by Hydrophilic/Hydrophobic Polymer Brushes

Polymer brushes, an optimal method for surface modification, have garnered significant interest due to their potential in surface wettability and functions regulation. This review summarizes the recent advancements in functional polymer brush surfaces based on surface wettability regulation. First, the fundamental structure and fabrication methods of polymer brushes, emphasizing the two primary strategies, "grafting-to" and "grafting-from", were introduced, and special attention was accorded to the method of subsurface-initiated atom transfer radical polymerization (SSI-ATRP) for the construction of mechanically robust polymer brushes. Subsequently, we delved into the attributes of the stimuli-responsive polymer brush surface, which can effectuate reversible surface wettability transitions in response to external stimuli. Then, this review also offered an in-depth exploration of the potential applications of polymer brushes based on their surface wettability, including lubrication, drag reduction, antifouling, antifogging, anti-icing, oil-water separation, actuation, and emulsion stability. Lastly, the challenges of polymer brush surfaces encountered in practical applications, including mechanical strength, biocompatibility, recyclability, and preparation efficiency, were addressed, and significant achievements in current research were summarized and insights into future directions were offered. This review intends to provide researchers with a comprehensive understanding of the potential applications of polymer brushes based on surface wettability regulation, and with the development of the polymer brush preparation technology, it will be anticipated that they will assume increasingly pivotal roles in various fields.

Grafting of Porous Conductive Fiber Mats with an Antifouling Polymer Brush by Means of Filtration-Based Surface Initiated ATRP

This work addresses the challenge of surface modification of porous, electrospun fiber mats containing an insoluble conducting polymer coating. Herein, a novel methodology of grafting a polymer brush onto conducting polymer fiber mats is developed that employs filtering of the polymerization solution through the fiber mat. An electrospun sulfonated polystyrene-poly(ethylene-ran-butylene)-polystyrene (sSEBS) fiber mat is first coated with a layer of conducting copolymer bearing an Atom Transfer Radical Polymerization (ATRP) initiating functionality (PEDOT-Br). The surface-initiated ATRP from the fibers' surface is then carried out to graft a hydrophilic polymer brush (poly(ethylene glycol) methyl ether methacrylate) by means of filtering the polymerization solution through the fiber mat. Scanning electron microscopy (SEM) images reveal a progressive change in the morphology of the fiber mat surface with the increasing volume of the filtrated polymerization solution, while energy dispersive X-ray spectrosdcopy (EDX) spectra show a change in the atomic oxygen to sulfur (O/S) ratio, therefore confirming the successful grafting from the fibers' surface. The conductive fiber mat grafted with hydrophilic brushes shows a 20% reduction in the non-specific adsorption of bovine serum albumin (BSA) compared to a pristine fiber mat. This study is a proof-of-concept for this novel, filtration-based, surface-initiated polymerization methodology.

Polyzwitterions: controlled synthesis, soft materials and applications

Polyzwitterions refer to polymers containing both positive and negative charged groups in one side chain, which have shown unique physicochemical properties and significant potential in diverse applications due to their amphiphilic and net-neutral charged properties. This review aims to highlight the recent advances in the design and synthesis of polyzwitterions including direct polymerization of zwitterionic monomers and deionization of polymers. Furthermore, the formation of polyzwitterion based soft materials such as nanoparticles by self-assembly, hydrogels, coatings and polyzwitterion brushes, as well as the influence of the microstructure on their properties and applications are discussed. The potential applications of polyzwitterions in drug delivery, antifouling, lubrication, energy storage and antibacterial are also summarized. Finally, the prospects of polyzwitterions are proposed.

"Coir Raincoat"-Boosted Biomimetic Hydrogel for Efficient Solar Desalination and Wastewater Purification

Solar-driven interfacial evaporation is an efficient method for purifying contaminated or saline water. Nonetheless, the suboptimal design of the structure and composition still necessitates a compromise between evaporation rate and service life. Therefore, achieving efficient production of clean water remains a key challenge. Here, a biomimetic dictyophora hydrogel based on loofah/carbonized sucrose@ZIF-8/polyvinyl alcohol is demonstrated, which can serve as an independent solar evaporator for clean water recovery. This special structural design achieves effective thermal positioning and minimal heat loss, while reducing the actual enthalpy of water evaporation. The evaporator achieves a pure water evaporation rate of 3.88 kg m-2 h-1 and a solar-vapor conversion efficiency of 97.16% under 1 sun irradiation. In comparison, the wastewater evaporation rate of the evaporator with ZIF-8 remains at 3.85 kg m-2 h-1 for 30 days, which is 16.3% higher than the light irradiation without ZIF-8. Equally important, the evaporator also showcases the capability to cleanse water from diverse sources of contaminants, including those with small molecules, oil, heavy metal ions, and bacteria, greatly improving the lifespan of the evaporator.

Enrichment of Nutmeg Essential Oil from Oil-in-Water Emulsions with PAN-Based Membranes

This study used polyacrylonitrile (PAN) and heat-treated polyacrylonitrile (H-PAN) membranes to enrich nutmeg essential oils, which have more complex compositions compared with common oils. The oil rejection rate of the H-PAN membrane was higher than that of the PAN membrane for different oil concentrations of nutmeg essential oil-in-water emulsions. After heat treatment, the H-PAN membrane showed a smaller pore size, narrower pore size distribution, a rougher surface, higher hydrophilicity, and higher oleophobicity. According to the GC-MS results, the similarities of the essential oils enriched by the PAN and H-PAN membranes to those obtained by steam distillation (SD) were 0.988 and 0.990, respectively. In addition, these two membranes also exhibited higher essential oil rejection for Bupleuri Radix, Magnolia Officinalis Cortex, Caryophylli Flos, and Cinnamomi Cortex essential oil-in-water emulsions. This work could provide a reference for membrane technology for the non-destructive separation of oil with complex components from oil-in-water emulsions.

Fabrication of a poly(N-isopropylacrylamide)-grafted alginate composite aerogel for efficient treatment of emulsified oily wastewater

The treatment of emulsion wastewater poses significant challenges. In this study, a novel porous material, namely esterified bagasse/poly(N, N-dimethylacrylamide)/sodium alginate (SBS/PDMAA/Alg) aerogel, was developed for efficient demulsification and oil recovery. By grafting a poly(N-isopropylacrylamide) (PNIPAM) brush onto the SBS/PDMAA/Alg skeleton through free radical polymerization, the resulting aerogel exhibits both surface charge and a molecular brush structure. The aerogel demonstrates remarkable demulsification efficiency for cationic surfactant-stabilized emulsions at various concentrations, achieving a demulsification efficiency of 95.6% even at an oil content of 100 g L-1. Furthermore, the molecular brush structure extends the application range of the aerogel, enabling a demulsification efficiency of 98.3% for anionic and non-ionic surfactant-stabilized emulsions. The interpenetrating polymer network (IPN) structure formed by SBS, PDMAA, and alginate enhances the mechanical stability of the aerogel, enabling a demulsification efficiency of 91.3% even after 20 repeated cycles. The demulsification ability of the composite aerogel is attributed to its surface charge, high interfacial activity, and unique brush-like structure. A demulsification mechanism based on the synergistic effect of surface charge and molecular brush is proposed to elucidate the efficient demulsification process.

Direct-coating of cellulose hydrogel on PVDF membranes with superhydrophilic and antifouling properties for high-efficiency oil/water emulsion separation

As a well-known natural and innocuous plant constituent, cellulose consists of abundant hydroxyl groups and can tightly adsorb onto material surfaces hydrogen bonding, resulting in a superhydrophilic surface. In this work, the hydrophobic polyvinylidene fluoride (PVDF) membranes were modified by immersing them in cellulose hydrogel using a simple one-step process. The modified PVDF membrane exhibited excellent resistance to fouling and oil adhesion, making it highly effective in separating various oil-in-water emulsions. The cellulose-modified PVDF membranes achieved a high oil rejection rate (>99 %) and a maximum separation flux of 2675.2 L·m-2·h-1. Furthermore, even an oil-in-water emulsion containing bovine serum albumin maintained a steady permeation flux after four filtration cycles. Additionally, these cellulose-modified PVDF membranes demonstrated excellent underwater superoleophobicity across a wide range of pH levels and high saline conditions. Overall, these cellulose-modified superhydrophilic PVDF membranes are sustainable, environmentally friendly, easily scalable, and hold great promise for practical applications in oily wastewater treatment.

Ultrasmall Cu3(PO4)2 Nanoparticles Reinforced Hydrogel Membrane for Super-antifouling Oil/Water Emulsion Separation

Membrane fouling is a persistent and crippling challenge for oily wastewater treatment due to the high susceptibility of membranes to contamination. A feasible strategy is to design a robust and stable hydration layer on the membrane surface to prevent contaminates. A hydrogel illustrates a distinct category of materials with outstanding antifouling performance but is limited by its weak mechanical property. In this research, we report a reinforced hydrogel on a membrane by in situ growing ultrasmall hydrophilic Cu₃(PO₄)₂ nanoparticles in a copper alginate (CuAlg) layer via metal-ion-coordination-mediated mineralization. The embeddedness of hydrophilic Cu₃(PO₄)₂ nanoparticle with a size of 3-5 nm endows the CuAlg/Cu₃(PO₄)₂ composite hydrogel with enhanced mechanical property as well as reinforced hydrate ability. The as-prepared CuAlg/Cu₃(PO₄)₂ modified membrane exhibits a superior oil-repulsive property and achieves a nearly zero flux decline for separating surfactant stabilized oil-in-water emulsions with a high permeate flux up to ∼1330 L m^-2 h^-1 bar^-1. Notably, it is capable of keeping similar permeate flux for both pure water and oil-in-water emulsions during filtration, which is superior to the currently reported membranes, indicating its super-antifouling properties.

A glutathione-responsive silica-based nanosystem capped with in-situ polymerized cell-penetrating poly(disulfide)s for precisely modulating immuno-inflammatory responses

HYPOTHESIS

Precise modulation of immuno-inflammatory response is crucial to control periodontal diseases and related systemic comorbidities. The present nanosystem with the controlled-release and cell-penetrating manner enhances the inflammation modulation effects of baicalein in human gingival epithelial cells (hGECs) for better oral healthcare.

EXPERIMENTS

We constructed a red-emissive mesoporous silica nanoparticle-based nanosystem with cell-penetrating poly(disulfide) (CPD) capping, through a facile in-situ polymerization approach. It was featured with a glutathione-responsive manner and instant cellular internalization capacity for precisely delivering baicalein intracellularly. Laboratory experiments assessed whether and how the nanosystem per se with the delivered baicalein could modulate immuno-inflammatory responses in hGECs.

FINDINGS

The in-situ polymerized CPD layer capped the nanoparticles and yet controlled the release of baicalein in a glutathione-responsive manner. The CPD coating could facilitate cellular internalization of the nanosystem via endocytosis and thiol-mediated approaches. Notably, the intracellularly released baicalein effectively downregulated the expression of pro-inflammatory cytokines through inhibiting the NF-κB signaling pathway. The nanosystem per se could modulate immuno-inflammatory responses by passivating the cellular response to interlukin-1β. This study highlights that the as-synthesized nanosystem may serve as a novel multi-functional vehicle to modulate innate host response via targeting the NF-κB pathway for precision healthcare.

Probing polymer brushes with electrochemical impedance spectroscopy: a mini review

Polymer brushes are frequently used as surface-tethered antifouling layers in biosensors to improve sensor surface-analyte recognition in the presence of abundant non-target molecules in complex biological samples by suppressing nonspecific interactions. However, because brushes are complex systems highly responsive to changes in their surrounding environment, studying their properties remains a challenge. Electrochemical impedance spectroscopy (EIS) is an emerging method in this context. In this mini review, we aim to elucidate the potential of EIS for investigating the physicochemical properties and structural aspects of polymer brushes. The application of EIS in brush-based biosensors is also discussed. Most common principles employed in these biosensors are presented, as well as interpretation of EIS data obtained in such setups. Overall, we demonstrate that the EIS-polymer brush pairing has a considerable potential for providing new insights into brush functionalities and designing highly sensitive and specific biosensors.

Antifouling enhancement of polyacrylonitrile-based membrane grafted with poly(sulfobetaine methacrylate) layers

In this work, zwitterionic polyacrylonitrile (PAN)-based membranes were synthesized via surface grafting strategy for improving the antifouling properties. The copolymer membrane consisting of PAN and poly(hydroxyethyl methacrylate) segments, was cast via nonsolvent induced phase separation, and then treated with acryloyl chloride to tether with carbon-carbon double bonds. Zwitterionic poly(sulfobetaine methacrylate) (PSBMA) layers were grafted onto membrane surface via concerted reactions of radical grafting copolymerization and quaternization with 2-(dimethylamino)ethyl methacrylate) and 1, 3-propanesultone (1, 3-PS) as the monomers. The grafting degree (GD) of PSBMA layers increases with the incremental content of monomers, leading to the enhancement in membranes surface hydrophilicity. The permeation experiments show that the flux of the zwitterionic membrane increases and then decreases with the increasing GD value, because of the surface coverage of PSBMA layers. The zwitterionic membrane has excellent separation efficiency for oil-in-water emulsion, with the rejection of a higher value than 99%. The irreversible membrane fouling caused by oil adsorption has been suppressed, as proved by the cycle-filtration tests. These outcomes confirm that oil-fouling resistances of membranes are improved obviously by the surface grafting of zwitterionic PSBMA layers.

Durable, magnetic-responsive melamine sponge composite for high efficiency,in situoil-water separation

The development of durable and high-performance absorbents forin situoil-water separation is of critical importance for addressing severe water pollution in daily life as well as for solving accidental large-scale oil spillages. Herein, we demonstrate a simple and scalable approach to fabricate magnetic-responsive superhydrophobic melamine sponges byin situdeposition of PDA coatings and Fe₃O₄nanoparticles, followed by surface silanization with low surface energy 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PTOS) layer. The prepared melamine sponge composite (PTOS-Fe₃O₄@PDA/MF) not only exhibits a very high water contact angle of 165 ± 1.5° and an excellent ability to uptake a variety of oils and organic solvents (e.g. up to 141.1 g/g for chloroform), but also shows robust durability and superior recyclability. The PTOS-Fe₃O₄@PDA/MF sponge can also efficiently separate oils (or organic solvents) and water, as demonstrated by different model systems including immiscible oil-water solution mixture and miscible water-oil (W/O) emulsion (stabilized by surfactants). Furthermore, the PTOS-Fe₃O₄@PDA/MF sponge is able toin siturecover organics from water using a peristaltic pump, which gives it significant advantages over other traditional batch processes for oil-water separation. We believe that the PTOS-Fe₃O₄@PDA/MF sponge provides a very promising material solution to address oil-water separation, especially for the large-scale problems that have been long-time challenges with conventional sorption methods.

Preparation of Multipurpose Polyvinylidene Fluoride Membranes via a Spray-Coating Strategy Using Waterborne Polymers

As reported herein, the waterborne polymers poly(glycidyl methacrylate-co-poly(ethylene glycol) methyl ether methacrylate) P(GMA-co-mPEGMA) and polyethyleneimine (PEI) were used to prepare multipurpose polyvinylidene fluoride (PVDF) membranes via a direct spray-coating method. P(GMA-co-mPEGMA) and PEI were alternately sprayed onto the PVDF membrane to yield stable cross-linked copolymer coatings. The successful coating of polymers onto the membrane surface was verified by scanning electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy characterization. The coated membrane exhibited oil rejection rates that exceeded 99.0% for oil water mixture separation and 98.0% for oil/water emulsion separation. The flux recovery ratio reached 96.7% after bovine serum albumin filtration and washing with water. The removal efficiencies of the coated membrane M3 for Congo red, methyl orange, methylene blue, and crystal violet, Pb(II), Cu(II), and Cd(II) were 82.4, 83.9, 6.3, 26.8, 90.6, 91.3, and 86.2%, respectively. Thus, it can be used for the removal of dyes and heavy metal ions from wastewater. The antibacterial activities of the coated membranes were also confirmed by the inhibition zone tests and confocal laser scanning microscopy analysis. In addition, the cross-linking strategy provides the coated membranes with excellent durability and repeatability. More importantly, the use of water as the solvent can ensure that the application of these membrane coatings proceeds via a very safe and environmentally friendly coating process.

Direct fluorination as a one-step ATRP initiator immobilization for convenient surface grafting of phenyl ring-containing substrates

Direct fluorination is proposed as a one-step ATRP initiator immobilization and the C–F added on the phenyl ring is demonstrated to be more suitable for initiation of ATRP.